Constant speed drive units are commonly found in aircraft for driving alternators and hydraulic pumps from main engine shaft rotation. One such unit is disclosed in Gantzer U.S. Pat. No. 3,365,981 granted Jan. 30, 1968.
In such units which are normally engaged with the main engine shaft at all times, there has been a disconnect feature for emergency use usually including a solenoid actuatable from the cockpit and a thermal coupling actuated automatically in the event of overheating of the transmission. A solution to a problem arising when the disconnect is actuated at low speeds is discussed in Schmohe U.S. Pat. No. 4,042,088 issued Aug. 16, 1977. Attachment of the constant speed drive unit to an engine housing and the provision of a retractable shaft is disclosed in the Schmohe U.S. Pat. No. 4,195,718 issued Apr. 1, 1980.
In these prior art disconnect devices, the specially shaped screw thread on the axially slidable sleeve which carries the clutch teeth for the driven member functions satisfactorily at shaft speeds of up to approximately ten-thousand rpm. At higher speeds, the plunger which is solenoid released, does not reliably engage the threads on the axially slidable sleeve and the disconnect function is sometimes not realized.